This invention relates to wall anchors for securing a support fastener and particularly to a cylindrical wall anchor with an outer thread for tapping into wall material such as dry wall, sheet rock and wood comprising the surface material of a hollow "wall" or similar structure. It especially relates to the construction of the distal end of the anchor which provides a circular sawing tip instead of a drill.
Prior art anchors, best typified by the self-drilling inserts disclosed in U.S. Pat. Nos. 4,601,625; 5,039,262; and 5,160,225; provide a closed end drill tip which is not desirable because of the heat of friction generated between the drill and the wall material and because the wall material is pushed and compressed during the drilling process resulting in breakage of the wall material around the bore at the rear surface of the wall and thus in a weakening of the wall's capacity to retain the anchor under stress. When used to penetrate wood panelling, the wood tends to split.
U.S. Pat. No. 5,234,299 to Gianuzzi discloses an open end drill tip with a pair of saw teeth in a saw-toothed configuration which, for the most part, eliminates generating heat by the typical drill tip. However, that anchor retains the concept of drilling by providing a tapered cylindrical surface to maintain the circularity of the drilled hole, by outward radial compression against the bank of the hole, before it is tapped by the thread on the shank portion of the anchor. Also, the saw-toothed configuration has the leading; i.e., cutting edge of each revolving tooth of the drill cutting material from the tip of each saw tooth to the pointed valley where it meets the trailing edge of the next saw tooth. This results in material build-up between the teeth and surface of the hole as it is being drilled because some of the cut material is squeezed into the pointed valley which is a circumferentially limited access area to the central bore.
It is an object of this invention to provide an outwardly threaded insert which has a cylindrical body with an axial through bore, a flange at the end of its proximal extension and a circular saw tip at the end of its distal extension for cutting a hole in the wall and permitting the wall material around which the tip has sawed to enter the axial bore so as not to be pushed and compressed and to "explode" out of the rear surface of the wall or otherwise weaken the seat of the anchor when in place.
In order to eliminate drilling, the circular saw tip of the invention has, in the instance disclosed in application Ser. No. 07/965,735, filed Oct. 23, 1992, been configured to provide the tips of saw teeth separated by flat or curved valleys which separate the sawing action of the revolving teeth to provide revolving spaces for the cut wall material to enter the through bore instead of being pushed to the outside. Optionally and in some applications, preferably, the thread of the anchor of the invention with the just described configuration extends fully between the distal and proximal ends so that tapping immediately follows the sawing action of the circular sawing to prevent any drilling to occur as in Gianuzzi U.S. Pat. No. 5,234,299 with his cylindrical guide surface.
In another embodiment of this invention, it is contemplated to provide a certain amount of outward radial compression between the anchor and wall material as the turning anchor taps the wall material and in this respect, a flat band-shaped compressor or what may be called a wedge strip is provided between the turns of the spiral thread of the anchor. In this construction, the compression between the anchor and wall between the turns of the spiral of the thread adjacent the flanged proximal end of the anchor tightens the seat of the anchor as by wedging.
In yet another embodiment of the invention, drilling and its consequent compression of the sawed material is eliminated both by spacing the saw teeth to provide passage for the loosened material between the teeth and by disposing the cutting edges of the saw teeth outside the outer diameter of the distal end of the anchor. In this construction, the sawed hole is wider than the distal end of the anchor and is, therefore, not affected by the surface of the anchor end. This construction has been designed for penetrating both hard wall material, such as wood and wall board. In the former instance, the anchor is preferably made of zinc.
In a surprising development of the invention, it has been found that a saw tipped anchor having a single saw tooth saws the hole for the anchor seat more efficiently than anchors with plural saw teeth in any configuration. It is believed that this is so because the configuration of the end of the through bore at the saw toothed end is slanted across the anchor axis so that there is more area for the cut wall material to enter. In this embodiment of the invention, the slanted aperture may be made more angled or less angled and the thread may be made to extend across a very extended aperture slanted through an obtuse angle to the axis of the bore.
It is contemplated by this invention that the flanged end of the insert is provided with a recess for receiving a drive tool, such as a power driven screw driver, for rotating the saw-tipped end against and through the wall board and that the interior of the axial bore of the insert is splined along its proximal extension so that a screw fastener may tap the splines as it is screwed into the insert with the flanged end of the insert within the material at the front surface of the wall board. It is also contemplated by this invention that the saw-tipped distal extension which has captured the sawed material passed the teeth of the saw, extends passed the rear surface of the wall board by a distance substantially equal to the thickness of the wall board. Resultingly, the screw fastener, which may be longer than the width of the wall board, after tapping into the splines of the axial bore, which extend from the flanged end of the insert a distance substantially equal to the thickness of the wall board, may then thread into the captured material or act to push the material out of the saw-tipped end of the anchor.
In a preferred embodiment of the invention, the outer diameter of the proximal extension increases from its juncture with the distal extension to its flanged end, while the saw-tipped distal extension of the insert comprises a straight cylinder with a slightly smaller outside diameter than the increasing outside diameter of the flanged proximal extension.
The cylindrical body may be outwardly threaded substantially along its entire length with the height of the thread increasing from the saw-tipped end to the flanged end inasmuch as the sawing action through the wall, rather than drilling, facilitates a quick insertion which is not diminished by the entry of the threads into the wall material surrounding the hole. The increase in the height of the thread from distal end to proximal end together with the increase in diameter of the proximal extension results in a gradual increase in the size of the tapping in the wall material to more gently push the wall material radially about the increasing height of the thread around the insert, thus, again avoiding "exploding" the wall material about the insert during insertion while providing a strong grip between the wall material and insert when in place.
It is also contemplated within the invention to provide a relatively thick cylindrical wall for the saw-tipped distal extension for the sawing operation.
It is yet another object of the invention to provide a flange for the proximal end of the insert which provides anti-rotational lock elements comprising tabs which are integral with the flange and which are axially bendable from a position away from the front surface of the wall in which the insert has been screwed to a position within the wall material where the tabs act as locking elements against rotation which may be caused by the turning of a screw fastener within the insert in either direction.
In one modification of the invention, the saw-toothed end is provided with forwardly extending teeth for sawing through the wall board and with secondary teeth disposed rearwardly and radially inwardly of the forward teeth for mashing the wall board material to assure that the material will not create a blockage of the axial bore. In the embodiment disclosed, the cross-section of the saw-toothed end is octagonal and provides the sawing teeth on a circumference of rotation with a larger diameter than the circumference of rotation of the mashing teeth.
A preferred embodiment of the invention, disclosed in application Ser. No. 07/965,735, filed Oct. 23, 1992, resulted from the discovery that the provision of but two saw teeth disposed 180.degree. to one another about the circumference of the saw-toothed end and separated by flat valleys facilitated the cutting operation at the surface of the wall board and made a cleaner cut through the wall board than the provision of three, four or more cutting teeth. Testing with an insert having two teeth so disposed, surprisingly resulted in the sawed material entering the axial through bore at the saw-toothed end more readily so that there was less material being pushed to the rear surface of the wall. Resultingly, there is less or no tear at the rear surface of the hole. While three or four teeth at the saw-tooth end works very well, it is theorized that a greater number of rotating teeth presents a circular knife to the wall board material being sawed and that fewer teeth present interrupted cutting or slicing edges which more readily permit the disposition of the sawed material into the bore at the saw-toothed end thus presenting less resistance to the rotating teeth.
Specially configured saw teeth disposed radially outwardly of the anchor body and slanted to lead cut material into the anchor through bore provides an anchor for sawing through wood or wall board.
Furthermore, and as discussed above, a further preferred embodiment of the invention is embodied in an anchor with but a single saw tooth, formed as the slanted surface of the aperture at the end of the through bore, which increases the area of the through bore opening at the distal end for wall material to enter.
It has also been found that the disposition of the thread around the body of the insert close to the saw-toothed end results in a pulling action on the insert just as the saw teeth enter the wall and thus a quicker insertion.
In a modification of the invention, the concept of sawing a hole through wall material and providing a tight, wedged seat with the action of the spiral thread and wedge band, is combined with a hook integrally formed at the proximal end of the anchor. The bore may extend from a closed proximal end where the hook is provided to the open distal end provided with the circular saw. The hook insert may be used in ceilings as well as in walls.
The inventive anchors as disclosed are designed for being molded of strong plastic materials such as nylon or a mixture of nylon and KEVLAR (a trademark of DuPont) combined but which may also be made of less strong plastics inasmuch as the friction normally resulting because of drilling operations of prior art inserts, is diminished because of the saw-tipped end of the insert of the invention. These inserts may also be cast in zinc .